Sensors are typically used for measuring a physical or chemical quantity such as temperature, pH, pressure, volume, and converting this data into another form, such as an electrical signal. Early systems having sensors required a technician to physically attend to the sensor to control, monitor, and acquire data from the sensor; e.g., a utility meter. Systems were later developed to communicate electrically with the sensors for providing the control, monitoring, and data acquisition functions. Conventional systems required costly wiring to each sensor.
With the development of wireless communication means, management of the sensors, i.e., providing the control, monitoring, and data acquisition functions, could be performed remotely. Modems are typically used as a means for inexpensive data communication. A modem is referred to herein as a device to connect two hosts through a data link. Modems typically convert signals produced by one type of device, e.g., a computer, to a form compatible with another device, e.g., a telephone. Many applications use modems connected to a telephone line accessible through a public switched telephone network (PSTN) to pass the onsite sensor data to an applications controller, typically a central management server. PSTN refers to the international public telephone system that carries analog voice data. The term modem stands for mo(dulator)-dem(odulator) since a stream of digital data or binary bits (0's and 1's) is modulated for transmission into an analog signal within the bandwidth of the PSTN and the received analog signal is demodulated back to digital data.
With the advent of the personal computer (PC), applications were developed to more easily enable a user to interface the PC to the modem for communication to the PSTN. A set of predefined commands, known as “the AT command set” for modems was initially developed by the Hayes Micro Computer Company in the mid 1980's to control their proprietary modem equipment used for connecting data terminals to host computing devices over the public telephone network. The AT command set is now the industry standard adopted by most modem manufacturers for controlling modems and serial data transmission over telephone lines. The AT command set has a string of characters for each command, preceded by the prefix “AT”, for sending instructions to the modem. The original AT Command set has been augmented many times as modem speeds and feature sets have increased. Special commands have been added by many vendors to control new features of their wired and wireless communication products.
More recently, the high production volumes and declining costs of cordless telephone technologies have made it cost effective to interconnect clusters of equipment together locally using wireless networks. As a result, the control, monitoring, and acquisition of data from remote sensors and other equipment from distant control centers using telephone and data networks has become more feasible. The cost of installing and maintaining the telephone lines or the wide-area data connections, however, is still prohibitive for low speed or occasional use communications. In addition, as the number of sensors increases, the cost and time required to control, monitor, and acquire data from the sensors also increases.
FIG. 1 is a block diagram depicting an exemplary prior art system 10 for applications using wireless devices such as modems for local data communications. The system 10 has two sensor-based nodes 14a, 14b, one corresponding to a sensor 16a and another for a sensor 16b. Although sensors 16a, 16b are shown, other non-sensors devices which require data management may be used. Similar prior art systems can include any number of sensor nodes, and are not limited to two such nodes. System 10 typically includes a microprocessor-based remote host controller 12a for providing system control for a corresponding node 14a in system 10. An identical remote host controller 12b is shown for a node 14b for sensor 16b. System 10 includes a requesting applications controller 30 which typically is a server that originates data requests to nodes 14a, 14b. 
Each remote host controller 12a, 12b typically includes a microprocessor, random access memory, non-volatile memory, and input and output signal interfaces. The remote host controllers 12a, 12b provide control based on an application program loaded therein through a loading means (not shown). The application program for each remote host controller 12a, 12b is typically loaded as firmware stored in the non-volatile memory of the system, but is not limited to this form.
As shown in the system in FIG. 1, each remote host controller 12a, 12b interfaces with a corresponding wireless device 20a, 20b via a data interface shown as serial port 26a, 26b. Each wireless device 20a, 20b has a pre-determined protocol to enable communication with its corresponding remote host controller 12a, 12b. The protocol may be a defined command set and syntax for every command, or through addressable register settings of each remote host controller 12a, 12b. Each remote host controller 12a, 12b can be programmed to manage or control different parts of the system via a corresponding I/O interface 28a, 28b with the sensor(s) 16a, 16b. Each I/O interface 28a, 28b typically provides digital and analog interfaces for sensor(s) 16a, 16b. Sensor(s) 16a, 16b include, for example, but are not limited to, switches, meters, signal lights, status, and measurement indicators. Depending on the sensor equipment provided, each remote host controller 12a, 12b can be programmed by a user for various functions, for example, switching lights on and off through a digital I/O interface, polling temperature readings through analog to digital converter circuitry, or interacting with an operator on site through a user interface.
When data communication is required which is event driven or pre-scheduled, the remote host controller 12a, 12b typically issues commands to its connected wireless device to initiate a communication session with another wireless device. For applications using a wireless device for data communication, the microprocessor-based remote host controller 12a, 12b executes its stored application program for managing all necessary functions and for preparing a status report to be forwarded to the higher level requesting applications controller 30. The applications controller 30 interfaces with a wireless device 20c via a data interface shown as serial port 26c. The report is typically sent upon request through a wireless link to the wireless device 20c and forwarded via the data interface to application controller 30.
The wireless devices 20a, 20b, 20c in the system in FIG. 1 have usually been implemented as telephone line modems. Using existing methods for telephone line modems, a dial-up connection is required before reading data or sending control information to a remote device. For requesting a reading of a sensor such as one of the sensor(s) 16a, 16b, application controller 30 must “call” the corresponding wireless device 20a, 20b using the wireless device 20c and request the called device to read the corresponding sensor and return the requested data. An exemplary sensor reading process for the prior art system 10 requires the following steps: making a call using a modem ATD command; connecting after a training session; the calling wireless device 20c sends a request for a sensor reading to one of the wireless devices 20a, 20b; the called device 20a or 20b sends the request to the corresponding remote host controller 12a or 12b which reads the corresponding sensor 16a or 16b. The sensor reading is then coupled back to the calling device 20c via the called device 20a-20b, and finally the link is disconnected. This procedure is slow and may require one or more seconds to complete.
A drawback of the system shown in FIG. 1 is that, when a application controller 30 needs to collect data from hundreds of sensors via their corresponding wirelessly linked device, the application controller 30 must separately “call” and establish a connection to each wireless device 20a, 20b, etc. in order to obtain the requested data. Each connection requires repeat of the above sensor reading process which requires a few seconds of time for each sensor. This time is required for each sensor, even if only a few bytes of data are requested from each sensor. A need exists therefore to reduce the time required to collect data from a large number of wirelessly linked devices.
In parallel with this growth in speed and complexity of communications, embedded control of processes and functions, via analog and digital sensors and actuators, in machines and other devices has expanded rapidly. Typically remote host microcontrollers are needed for each wireless device and sensor node. A need exists to reduce cost and device size by eliminating separate host microcontrollers for each sensor node. A wireless embedded communications system and method is therefore needed which solves the above described drawbacks of the prior art.